The Science & Technology
of Glass
Cambridge - Monday 4th to
Wednesday 6th September 2017

Shuchi Vaishnav

article posted 22 May 2017

Shuchi holds one Masterís degree in Nuclear Reactor Physics and Engineering and another Masterís degree in Nuclear Energy from INSTN, CEA, France and University of Delhi, India respectively. She is currently pursuing her PhD at Materials & Engineering Research Institute at Sheffield Hallam University, UK. Her research topic deals with enhancement of silicate and borosilicate glass systems used for radioactive waste immobilization with focus on high level waste containing high levels of sulphate ions. Her research interest lies in studying structural changes in waste glasses using various spectroscopic techniques. Previously she has served as nuclear reactor researcher in EDF R&D, France; IGCAR-Kalpakkam, India; and IPR-Fusion ITER unit, India/France.

The Role of BaO Modifier in Silicate and Borosilicate Glass Systems with High Sulphate Solubilities
Shuchi Vaishnava*, Alex C. Hannonb, Emma R. Barneyc, John V. Hannad & Paul A. Binghama

The high content of sulphate (SO42- ) ions present in some high-level radioactive waste (HLW) and its poor solubility in the vitrified waste borosilicate glass matrix (-as low as 1 wt%) can result in processing problems or in high final waste form volumes due to the need for dilution. Secondary sulphate salt layer formation not only limits the waste loading but creates a possible pathway for radionuclides to enter the biosphere and must therefore be avoided. The study of sulphate behaviour in HLW glass formulations is very challenging due to presence of many elements in the vitrified wasteform. Therefore, to develop a better understanding of the mechanisms underlying the solubility of sulphate, we have studied in the structure of sulphate doped binary, ternary and quarternary silicate and borosilicate glass systems, in addition to complex borosilicate glasses that are broadly representative of real-world radioactive waste vitrification practices. Ternary formulations containing BaO were particularly interesting as they can incorporate high (5 wt%) levels of sulphate compared with other alkali-alkaline earth silicate and borosilicate glass systems with no clear evidence of phase separation. Spectroscopic results from Raman spectroscopy; 29Si, 11B and 23Na-MAS NMR; and Neutron Diffraction have been considered, and will be presented here.

Keywords: Sulphate; Silicate glasses; Borosilicate glasses; Alkaline- Earth Oxide; Nuclear waste; Raman Spectroscopy; NMR; Neutron Diffraction

Figure 1: The Q3/Q2 ratio increases in sulphate doped glasses as shown by Raman spectroscopy and 29Si Ė MAS NMR. Sulphate incorporation leads to polymerisation of glass network. The Na2O-BaO-SiO2 (NaBaSi) glass shows minimal change in Q3/Q2 ratio on sulphate doping, despite high sulphate incorporation.

Figure 2: Centroid of fitted v1 S-O Raman band is influenced by network modifiers. Suggestive of partial stabilisation of SO42- tetrahedra by Ba2+ in Na2O-BaO-SiO2 (NaBaSi) but mostly by Na+ in Na2O-CaO-SiO2 (NaCaSi) glass system.

aMaterials and Engineering Research Institute, Sheffield Hallam University, Sheffield S1 1WB, UK
bISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK
cFaculty of Engineering, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK
dDepartment of Physics, The University of Warwick, Coventry, CV4 7AL, UK